Field of Disclosure
The following relates generally to wireless communication, and more specifically to channel feedback reporting for shared frequency spectrum.
Description of Related Art
Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, single-carrier frequency-division multiple access (SC-FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
By way of example, a first wireless multiple-access communication system may operate according to a radio access technology (RAT), such as LTE, and may include a number of base stations, each simultaneously supporting communication for multiple communication devices, otherwise known as user equipments (UEs). A base station may communicate with UEs on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station). A second wireless multiple-access communications system may operate according to a different RAT, such as Wi-Fi, and may include a number of base stations or access points (APs), each simultaneously supporting communication for multiple mobile devices or stations (STAs). APs may communicate with STAs on downstream and upstream links. In some cases both types of communication systems may operate in the presence of one another and may use shared resources.
In a wireless local area network (WLAN), such as Wi-Fi, an AP may communicate with multiple STAs over a shared radio frequency spectrum. The STAs may use contention procedures that include communicating one or more control frames prior to establishing a communication link, such that confirmation of the communication link via exchange of control frames limits interference experienced by nearby communication devices. One example of such techniques include Request to Send (RTS) and Clear to Send (CTS) messaging, where, for example, a STA looking to communicate with another device (e.g., another STA or AP), may first send an RTS frame to the device. Once the recipient device receives the RTS frame, the recipient device may confirm the communication link by sending a CTS frame. After the CTS frame is received by the STA, the STA may then begin transmitting data to the recipient device. In this way, RTS/CTS messaging can reduce frame collisions by enabling a device, such as a STA or AP, to in essence clear the communication path before transmitting data to an AP or STA.
In an LTE network, a base station and a UE may communicate over a dedicated frequency spectrum or over different frequency bands of the radio frequency spectrum (e.g., a dedicated radio frequency band and a shared radio frequency band) of a cellular network. With increasing data traffic in cellular networks that use a dedicated (e.g., licensed) radio frequency band, offloading of at least some data traffic to a shared (e.g., unlicensed) radio frequency spectrum may provide a cellular operator with opportunities for enhanced data transmission capacity. A shared radio frequency spectrum may also provide service in areas where access to a dedicated radio frequency spectrum is unavailable. An LTE device that is configured for operation in shared frequency spectrum may be considered to be an LTE-Unlicensed (LTE-U) device. An LTE-U device may be configured for operation in dedicated radio frequency spectrum, using a standalone carrier in shared radio frequency spectrum, or using shared radio frequency spectrum in addition to dedicated radio frequency spectrum.
Prior to gaining access to and communicating over a shared radio frequency spectrum, a base station or UE may perform a listen before talk (LBT) procedure to contend for access to the shared radio frequency spectrum. This LBT procedure may be compatible with contention procedures used by Wi-Fi devices to gain access to the shared radio frequency spectrum. An LBT procedure may include performing a clear channel assessment (CCA) procedure to determine whether a channel of the shared radio frequency spectrum is available. Since a UE or base station first monitors the channel during the CCA to detect if the channel is occupied, a UE or base station may not win control of the channel with each LBT procedure
In some cases, a device, such as an LTE/LTE-U UE, may report control information (e.g. acknowledgement (ACK)/negative ACK (NACK), channel state information (CSI), etc.) periodically or aperiodically to a corresponding LTE/LTE-U base station. For periodic reporting, the UE may send the control information according to an interval, specified by the base station, while for aperiodic reporting the UE may send control information in response to receiving a trigger from the base station. However, as mentioned above, the UE may fail to win control of the channel after performing an LBT procedure for periods corresponding to the designated interval. Therefore, the UE may fail to transmit control information to the base station under various circumstances. In the case of aperiodic reporting, the UE may fail to report the control information until the UE performs a successful LBT procedure. Delayed or failed control feedback reports may prevent the network from developing current channel estimates resulting in decreased link performance or throughput.